Method of manufacturing oxidized lead powder



H. D. WILSON April 1, 1941,

METHOD OF MANUFACTURINQ OXIDIZED LEAD POWDER 1 Filed Oct. 23, 1936 2Sheets-Sheet l N Inventor, HARLAND D. WILSON April 1, 1941. H n wlLsoN2,237,043

METHOD OF MANUFACTURINQ OXIDIZED LEAD POWDER Filed Oct. 23, 1936 2Sheets-Sheet 2 f2" l.l

Y r IO N u N a S l Inventor: HARLAND D. W/LSON Attofneu.

Patented Apr. 1, 1941 METHOD OF MANUFACTURING OXIDIZED LEAD POWDERHarland D. Wilson, Indianapolis, Ind., assignor to Prest-O-Lite StorageBattery Corporation, Speedway, Indianapolis, Ind., a corporation ofIndiana Application October 23, 1936, Serial No. 107,2Q5

4 Claims.

My present invention relates to a continuous process of manufacturingoxidized or partially oxidized lead powder, and more particularly to aprocess in which lead pieces are subjected to attrition by rumbling themin a rotatable vessel or mill in the presence of a controlled current ofair or other oxidizing gas and under controlled temperature conditions.

In carrying out such a process, the product is obtained by first forminga brittle coating of oxide on the surfaces of the metallic lead piecesby bringing the current of air or other oxidizing gas into contact withthe metallic lead pieces at an elevated temperature. The coating thusformed is abraded off in the form of an extremely fine powder, either byattrition of the lead pieces or by the rubbing action of the interiorsurface of the rotating vessel with that portion of the lead mass withwhich it is in contact. Thus new surfaces of metallic lead are beingcontinually exposed to the action of the oxidizing agent, and, in turn,will be oxidized and abraded. The product thus formed may be removedfrom the mill by the current of oxidizing gas or by any other suitablemeans.

The frictional heat produced within the mill, plus the heat liberated bythe oxidation reaction, will be more than sufficient to maintain theinterior mill temperature at the desired elevated value without theaddition of heat from external sources.

I have found that in practice the process may be carried out moreefiiciently, and a more nearly uniform product obtained by maintainingthe interior mill temperature constant and at as high a value as ispossible without causing the lead pieces to melt.

In processes heretofore used (as, for example, that disclosed in U. S.Patent No. 1,584,150 issued May 11, 1926, to Genzo Shimadzu) it has beenproposed to control the temperature within the mill by varying the speedof the mill, the amount of oxidizing gas passing through the mill, orthe amount of charge in the mill. In practice, however, it has beenfound desirable to maintain the mill speed and the volume of airconstant, with the result that temperature control has been effectedsolely by varying the amount of charge. However, because of the periodof time required for a variation in the amount of charge in the mill toeffect a change of temperature Within the mill, this method has not beenentirely satisfactory. Also, the efiiciency of the process has beensomewhat impaired, by reason of the. fact that in order to lower themill temperature it has been necessary to reduce the amount of charge,thus reducing the area of the lead surface available for oxidation.

One object of my invention is to provide a process of the type referredto above in which the temperature within the mill, including thetemperature of the lead masses undergoing attrition, may be controlledwithin narrow limits by a novel method and without the necessity ofvarying the operating conditions of the mill.

A further object of my invention is to provide an improved method of theforegoing type having a greater opera-ting efficiency and producing agreater yield of product than similar processes heretofore used.

Another object of my invention is to provide a method of producing anoxidized lead powder of a more nearly uniform character than hasheretofore been possible.

A further object of my invention is to provide an improved method ofproducing oxidized lead powder by the attrition process which isindependent of changes in climatic conditions to a greater degree thanprocesses heretofore used.

A further object of my invention is to provide a novel'apparatus forcarrying out the herein described method.

Other objects, features and advantages will be apparent as thedescription proceeds.

I have discovered that by impinging directly upon the rumbling pieces oflead-a small but continuous supply of water, a substantially largerquantity of lead pieces may be rumbled in the rotatable vessel with theresult that a substantially larger output per unit of time may besecured without a corresponding increase in temperature such as wouldresult if no water were used. Further, I have discovered that the milltemperature is rapidly responsive to changes in the volume of water sosupplied, a slight increase in the amount of water will cause thetemperature to drop, and conversely, a slight decrease will cause thetemperature to rise. By means of this very sensitive method oftemperature control, any tendency of the mill temperature to vary fromthe desired operating temperature can be readily and rapidly compensatedfor, and the temperature maintained constant within very narrow limits,the time lag between variations in water supply and their eifect uponthe temperature being of the order of two to three minutes, as comparedwith a lag of the order of twenty to thirty minutes where temperaturecontrol is effected by varying the amount of charge. In addition to thegreater yield mentioned above, the

elimination of temperature variations results in a more nearly uniformproduct. As a practical illustration, I have found that the normalcharge for a mill of the type disclosed in U. S. Patent No. 1,896,020,issued January 31, 19.33, to Genzo Shimadzu, having a diameter of aboutfour and one-half feet and a length of six feet, and through which airis being passed at the rate of about 470 cubic feet per minute, is about4,000 pounds.

temperature of the mill will normally be about Under these conditionsthe interior 410 F. However, by supplying small quantities of water inthe manner set forth above, I have found that the amount of the chargemay be increased to approximately 5,200 pounds without a resultingincrease in temperature. At the same time, the quantity of oxideproduced per day increased from 16,000 pounds to 20,000 pounds ofproduct having substantially the same physical and chemicalcharacteristics.

The quantity of water which is appropriate to be introduced is verysmall in comparison with the effect obtained, being of the order ofmagnitude of 100 to 600 cubic centimeters per minute for a charge" of5,200 pounds. Best results are obtained by impinging the water upon thetumbling charge at a number of different points so that contact of thewater with the charge is not confined to a single locality within thevessel. Small tubes discharging in different zones are a suitable meansof introduction.

The amount of water required for smooth operation'will vary from time totime, so that it is essential to provide a means of securing variationsin the rate of flow in accordance with practical requirements. Themoisture content of the air is considerably greater at some times thanat others, for example, on rainy days. It is also considerably greaterduring thesummer than during the winter.

The exact manner in which a small amount of water impinging upon thecharge in the rotating vessel efiects such a remarkable increase inefficiency of ODEIHJtlOIl'Of an oxide producing unit, or" serves as suchan extremely sensitive temperature regulator, is not fully understood".It may be that the effect is partially one of catalysis. Or it maybethat the eifect resides in the concentration of water vapor per unitvolume of space within the reaction vessel. When atmospheric air enterssuch a vessel, it quickly becomes expanded due to the elevatedtemperature ofthe charge, and due to this expansion the moisture densityper unit volume becomes considerably lower than in atmospheric air atroomtemperature. Experience has shown that operation of the oxideproducing process becomes unsatisfactory when the moisture content ofthe air reach'es'unusually low concentrations as, for example, in verycold winter weather; It may be, therefore, that the function of waterimpinged upon the charge is to increase the moisture density per unitvolume in the zone of reaction to a more efficient concentration. It isalso possible that one function of introduced water is the absorption ofheat at the point Where heat is liberated by friction and oxidation, theeffectiveness of water in this respect being due to its large latentheat of vaporization as well as'to its relatively high specific' heat.

In the annexed drawings, wherein I haveillustrated suitable apparatusfor carrying out my process; 7 Y j t Figure 1 is a'. side elevational'view partly in Section of an attrition mill;

Figure 2 is a sectional view of an air nozzle taken through the line 2-2of Figure 1;

Figure 3 is a schematic illustration of a complete installation forcarrying out my improved method, and

Figure 4 is a sectional view taken on the line 4-4 of Figure 3. I

Referring to the drawings, reference numeral l-ll designates generallyan attrition mill, preferably cylindrical in form, which is rotatablymounted by means of hollow trunnions H and I2 which are supported bybearings I3 mounted on foundations M. The means for causing rotation ofthe mill are not illustrated as they form no part of this invention, itbeing understood that any suitable means may be employed for thatpurpose. Lead lumps or balls are fed continuously by suitable feedingmechanism 15 to a screw conveyor l6 which in turn delivers them to theinterior of mill I0. Air is supplied to a header l1 positioned axiallyof the mill by means of a blower I8. Jets or nozzles [9 leading from theheader direct a plurality of streams of air atthe lead masses 20. Outlettrunnion l2 communicates with a conduit 2| through which the escapingair passes to a cyclone separator 22, thence through conduit 23 to adust collector 24. The dust free air is exhausted to the atmospherethrough opening 25, preferably located above roof 2-6. The powder fallsinto drums 21 located below the cyclone and dust collector,

For the purpose of supplying water to the interior of the mill, I haveprovided conduits 28 connected with a source of supply of water (notshown). Said conduits enter through header H and terminate at a pointadjacent the orifice of a nozzle 19 as shown in Figure 2. The quantityof Water passing into the mill is controlled by valves 29 and may bevisibly ascertained by means of sight gauges 30. Although forpurposes-of illustration, Ihave'shown but two water supply conduits, itis to be understood that, in practice-it is desirable to supply water tothe lead massesat many points,.as, for example, through each nozzle.

In operation, the millll! isrotated to cause abrasion of the surfacesof.the lead pieces which have been oxidized by exposure to the air at anelevated temperature. The powder thus'formed is carried by the aircurrent through trunnion H to the cyclone 22 where partial separationfrom the air is efiected. The powder remaining in the air is caught bydust coll'ecter 24 and falls into drum 21. New lead is continuouslyadded to the mill by feedingmeans 15 through screw conveyor F6. Thetemperature of the mill is readily controlled by manipulation of valves29) to increase or diminish the quantity of Water entering the mill. V

The advantages of my invention are now apparent. By the simple andeconomical expedient ofsupplying a small quantity of water to the leadmasses in the reaction zone of the vessel, I have been able to greatlyincrease the efficiency of the process andto obtain a product, theuniformity of which may be more readily maintained. Also I'havecompletely divorced the matter of temperature control from the variousother mill operating conditions, thereby permitting a more-j uniformyear-round operation. I have found-that best results are obtained whenthe water, probably in the form of an atomized spray, is" applieddirectly to the surfaces of the lead masses, as by being carried by theair-streams passing through jets I9, altho any other satisfactory meansfor applying the water to the lead masses may be employed.

The term oxidized lead powder as used herein is intended to mean theproduct of the herein disclosed process which, when carried out inaccordance with the preferred embodiment disclosed above, produces aproduct consisting essentially of an intimate mixture of extremelyfinely divided litharge (PbO) and metallic lead (Pb). A small percentageof finely divided suboxide of lead (PbzO) may be intermixed therewith.For storage battery purposes the desirable percentage oxidation,calculated as litharge, is 65%, but it will be readily understood thatthe degree of oxidation may be varied over a wide range by varying theoperating conditions, such as the temperature, amount of air, speed ofthe mill, amount of charge, etc. The term partially oxidized lead powderas used herein is intended to mean a lead powder, some of the particlesof which have been oxidized, but the total oxygen content of which isless than that of litharge.

The method and apparatus herein described are for purposes ofillustration only, and are not intended to limit the scope of myinvention. Many modifications will occur to those skilled in the art. Itis my intention that this patent shall cover all such modifications ascome within the scope of the appended claims.

Having thus fully described my invention, what I claim is:

1. The step in the method of manufacturing oxidized lead powder by theattrition process at a temperature above 212 degrees F. which consistsin apply a plurality of small streams of water to the surfaces of thelead masses undergoing oxidation and abrasion to control the temperaturethereof.

2. The method of manufacturing oxidized lead powder which consists inplacing pieces of lead in a rotatable drum, rotating the drum, supplyingan oxidizing gas to the drum to oxidize the surfaces of the lead pieces,abrading the oxide thus formed by attrition, applying water to thesurfaces of the lead pieces, and controlling the temperature of the leadpieces by regulating the quantity of water so supplied, the temperatureof said lead pieces being above the boiling point of the water.

3. The method of controlling the temperature of the interior of anattrition and oxidizing drum, said temperature exceeding 212 degrees F.which consists in introducing into the drum and onto the materialundergoing oxidation and attrition a stream of water, and regulating thequantity

